Cleaning of Stack Gases Containing High Concentrations of Nitrogen Oxides

Multistage gas absorption of 1–50% nitric oxide, nitrogen dioxide, and nitrogen tetraoxide from air with water or caustic solutions can produce colorless stack discharges. The rate at which NO is oxidized to No₂ in the gas phase and the solubility rate of No₂ in water or solution are highly concentration dependent so that reductions of stack gas concentrations of nitrogen oxides below approximately 200 ppm appear to be impractical. High efficiency absorption combined with elevated discharge of the cleaned, colorless gases is an acceptable method of air pollution control for many troublesome operations. Experiences in the fields of rocketry and nuclear energy are cited. Engineering modifications of metal pickling operations have been found especially helpful in producing effective control at an acceptable cost.     

On the Relation Between the Indoor and Outdoor Concentrations of Nitrogen Oxides

Simultaneous measurements were made of the concentrations of NO, NO₂, and CO inside and outside of a building. The building is located in the Los Angeles area, which is heavily polluted by photochemical smog, and the experiments were conducted at a time of the year when the pollutants in question tend to be high. The results shows that there is a direct relationship between the inside and outside concentrations, and that the phase lag between the concentrations depends principally on the ratio of the building volume to the ventilation rate. Although the outside concentrations of the pollutants in question did not follow the same pattern every day, peak concentrations seemed to be related to “rush-hour” traffic. By reducing ventilation rates during these periods, it may be possible to reduce the concentration peaks inside of the building. The building involved in the current study was not located in the immediate vicinity of heavy traffic, and the indoor concentrations of NO, NO₂, and CO did not appear to be very severe when compared to those defined by present air quality standards. Finally, the results support the belief that NO and O₃ do not co-exist indoors except in very small quantities.     

A New Catalytic Reactor for Nitrogen Oxides Removal

The body of information presented in this paper is directed to those individuals concerned with the catalytic NO_x removal reactor for a dirty (containing dust) flue gas. In the case of treating a dirty flue gas, the concentration of dust is the most important factor. While the dirty gas passes through the catalytic reactor, dust particles deposit and plug up the catalyst causing the reactor pressure loss to rise. As a result, the NO_x reduction efficiency decreases more and more, and continuous operation becomes impossible. A new type of NO_x removal reactor for dirty flue gas, the intermittent moving bed reactor, has been developed. The following characteristics have been evaluated: (1) method of calculating reactor pressure loss caused by dust particles, (2) static pressure distribution across the catalyst bed in the reactor, (3) method of evaluating uniform movement of catalyst and (4) reentrainment pattern of dust by catalyst movement. After carrying out various successful pilot plant tests, the information needed for construction and operation of a commercial plant has been developed.     

Considerations in Setting Standards for Oxides of Nitrogen

Since 1959 the California Department of Public Health has held responsibility for setting standards for ambient air quality and for motor vehicle emissions. The need for standards for oxides of nitrogen involves consideration both of direct effects and effects resulting from participation in photochemical smog reactions. This paper discusses the various effects of concern and describes the department’s program for establishing air quality standards which will become the basis for vehicle emission standards and serve as guides for control of other sources of oxides of nitrogen.     

A Comparison of Phenoldisulfonic Acid,Nondispersive Infrared,and Saltzman Methods for the Determination of Oxides of Nitrogen in Automotive Exhaust

The Saltzman Phenoldisulfonic Acid and Nondispersive Infrared methods have been compared for the determination of oxides of nitrogen in automobile exhaust. The main purpose of this investigation was to determine whether the Nondispersive Infrared method could be used as a possible replacement for the Saltzman method. Results show that the Nondispersive Infrared analyzer can be used to measure NO_x in exhaust gases with advantages over both the Saltzman and Phenoldisulfonic Acid methods. These advantages include simplicity, speed, less complicated analytical technique, and the fact that it is better adapted to be carried out by technicians at the test site.     

Technology Innovations and Experience Curves for Nitrogen Oxides Control Technologies

Abstract

This paper reviews the regulatory history for nitrogen oxides (NO_x) pollutant emissions from stationary sources, primarily in coal-fired power plants. Nitrogen dioxide (NO₂) is one of the six criteria pollutants regulated by the 1970 Clean Air Act where National Ambient Air Quality Standards were established to protect public health and welfare. We use patent data to show that in the cases of Japan, Germany, and the United States, innovations in NO_x control technologies did not occur until stringent government regulations were in place, thus “forcing” innovation. We also demonstrate that reductions in the capital and operation and maintenance (O&M) costs of new generations of high-efficiency NO_x control technologies, selective catalytic reduction (SCR), are consistently associated with the increasing adoption of the control technology: the so-called learning-by-doing phenomena. The results show that as cumulative world coal-fired SCR capacity doubles, capital costs decline to ~86% and O&M costs to 58% of their original values. The observed changes in SCR technology reflect the impact of technological advance as well as other factors, such as market competition and economies of scale.     

Measurements of Sulfur Oxides,Nitrogen Oxides,Haze and Fine Particles at a Rural Site on the Atlantic Coast

During August, 1982 and January and February, 1983, General Motors Research Laboratories operated air monitoring sites on the Atlantic Coast near Lewes, Delaware and 1250 km to the east on the southwest coast of Bermuda. The overall purpose of this project was to study the transformations of the principal acid precipitation precursors, NO _x and SO _x species, as they transport under conditions not complicated by emissions from local sources. In this paper, the measurements of gas and particulate species from Lewes are described and the composition and sources of sulfate aerosol, which is the most important haze-producing species, are investigated.

On the average, the total suspended particulate (TSP) concentration was 27.9 μg/m³ while the PM₁₀ (mass of particles with a diameter less than or equal to 10 μm) concentration was 22.0 μg/m³ or 79 percent of the TSP. The PM₁₀ consisted of 6.1 μg/m³ of coarse particles (CPM, diameter = 2.5 ? 10μm) and 15.9 μg/m³ of fine particles (FPM, diameter < 2.5 μm).

On a mass basis the most important constituents of the fine particulate fraction were sulfate compounds, 50 percent, and organic compounds, 30 percent. The mean light extinction coefficient corresponds to a visual range of 18-20 km. Most of the extinction can be attributed to the sulfate (60 percent) and organic carbon (13 percent). Particle size measurements show that the mass median aerodynamic diameter for both species is 0.43 μm. This is a typical size for a hydrated sulfate aerosol. For carbon, however, this is a larger size than previously reported and results in a more efficient light scattering aerosol. Principal component analyses indicate that coal combustion emissions from the midwestern U.S. are the most significant source of sulfate in Lewes during the summer and winter.     

Analysis of Mosses and Soils for Quantifying Heavy Metal Concentrations in Sicily: A Multivariate and Spatial Analytical Approach

- DOI: http://dx.doi.org/10.1065/espr2006.01.006 Background The use of vegetal organisms as indicators of contamination of the environment is partially replacing traditional monitoring techniques. Amongst the vegetal organisms available, mosses appear to be good bioindicators and are used for monitoring anthropogenic and natural fall-out on soils. This study has two objectives: the evaluation of the concentrations of heavy metals in soils and mosses of the Sicily Region, in Italy and the identification of the origin of fall-out of heavy metals. Methods Mosses and the surface soil were sampled at 28 sites, only the youngest segments of Hylocomium splendens and Hypnum cupressiforme, corresponding to the plant tissues produced during the last 3 years, were taken. The elements Cd, Cu, Ni, Pb and Zn were analysed by ICP-MS and Hg by AAS. Statistical analysis was by PCA and spatial representation by GIS. Results and Discussion In the mosses sampled in Sicily, the highest concentrations of Cd were found around the cities of Palermo and Messina. The highest concentrations of Hg were recorded in the northern part of the island between Trapani and Messina, similar to the distribution of Cu. Different areas with the highest concentrations of Ni were found near the south coast, in the vicinity of Palermo and around the Volcano Etna. The highest concentrations of Pb were found in the south-west coast near Agrigento, where important chemical plants and petroleum refineries are located. Except for a few locations, Zn fall-out was found to be evenly distributed throughout Sicily. Conclusion The sites where the concentrations of heavy metals cause greatest concern have been revealed by the PCA analysis and portrayed using GIS. Also of some concern is the diffuse and anthropogenic origin of Hg and Cd. The combined approach of using soil and mosses, together with pedological interpretation and application of multivariate statistical techniques has provided valuable insight into the environmental aspects of heavy metal deposition in a region of southern Europe. Recommendations and Outlook Further insight into the deposition of heavy metals will require more detailed sampling of soils and mosses in both new and previous study areas. This needs to be complemented by detailed pedological investigations in the study areas. Future research programmes will address these issues.     

Global Emissions of Nitrogen and Sulfur Oxides from 1860 to 1980

Statistical models have been developed that relate the rate of emissions of a pollutant to the rate of fuel consumption. These relations may be used to estimate emissions in other regions, or at other times, if fuel consumption data are available. This approach has been used to estimate global emissions of nitrogen and sulfur oxides in fossil fuel combustion at ten year intervals from 1860 to 1980. Emissions from each of the populated continents, i.e., North America, South America, Asia, Europe, Africa and Oceania from 1930 to 1980 are also presented. When averaged globally over the 1860 to 1980 period, sulfur emissions increased at the rate of 2.9 percent per year and the nitrogen emissions at the rate of 3.4 percent per year. The ratio of global sulfur emissions to nitrogen emissions has declined steadily; it was nearly 5 in the 19th century and became 3 by 1980. After the second world war, the most rapid increases in emissions have been registered in Asia, South America, and Africa.     

Development of Models for Predicting the Distribution of Indoor Nitrogen Dioxide Concentrations

Extensive data on residential indoor and outdoor NO₂ levels have been collected in a limited number of U.S. locations. To date, researchers have analyzed these data sets individually, but have not analyzed them in the aggregate. Results have not, therefore, been suitable for application in a nationwide exposure assessment. This paper presents an analysis of indoor and outdoor NO₂ field measurements from five U.S. metropolitan areas for homes with gas-fueled ranges and discusses potential applications of the results. Using linear regression analysis, the relationship between indoor NO₂ and various predictor variables was explored. Results indicated that ambient NO2 levels alone explain an estimated 37 percent of the variability in indoor NO₂ levels, that the relationship between indoor and outdoor NO₂ concentrations differs significantly from summer to winter months, and that homes with range pilot lights have indoor levels approximately 7 ppb greater than homes without pilot lights. A logistic regression model which predicts the distribution of indoor NO₂ levels based on ambient NO₂ concentrations was developed. Estimation and testing of the logistic model indicated good model performance. The model is particularly useful for addressing policy-oriented questions that involve the concept of "acceptable" threshold levels for human exposure to NO₂.     

Impact of Microenvironmental Nitrogen Dioxide Concentrations on Personal Exposures in Australia

ABSTRACT

Indoor and outdoor NO₂ concentrations were measured and compared with simultaneously measured personal exposures of 57 office workers in Brisbane, Australia. House characteristics and activity patterns were used to determine the impacts of these factors on personal exposure. Indoor NO₂ levels and the presence of a gas range in the home were significantly associated with personal exposure. The time-weighted average of personal exposure was estimated using NO₂ measurements in indoor home, indoor workplace, and outdoor home levels. The estimated personal exposures were closely correlated, but they significantly underestimated the measured personal exposures. Multiple regression analysis using other nonmeasured microenvironments indicated the importance of transportation in personal exposure models. The contribution of transportation to the error of prediction of personal exposure was confirmed in the regression analysis using the multinational study database.     

Consistency of Ozone and Nitrogen Oxides Standards at Tropospherically Relevant Mixing Ratios

Abstract

The absolute accuracy and long‐term precision of atmospheric measurements hinge on the quality of the instrumentation and calibration standards. To assess the consistency of the ozone (O₃) and nitrogen oxides (NO_x) standards maintained at the National Institute of Standards and Technology (NIST), these standards were compared through the gas‐phase titration of O3 with nitric oxide (NO). NO and O₃ were monitored using chemiluminescence and UV absorption, respectively. Nitrogen dioxide (NO₂) was monitored directly by laser‐induced fluorescence and indirectly by catalytic conversion to NO, followed by chemiluminescence. The observed equivalent loss of both NO and O₃ and the formation of NO₂ in these experiments was within 1% on average over the range of 40–200 nmol mol^?1 of NO in excess O3, indicating that these instruments, when calibrated with the NIST O₃ and NO standards and the NO₂ permeation calibration system, are consistent to within 1% at tropospherically relevant mixing ratios of O₃. Experiments conducted at higher initial NO mixing ratios or in excess NO are not in as good agreement. The largest discrepancies are associated with the chemiluminescence measurements. These results indicate the presence of systematic biases under these specific conditions. Prospects for improving these experiments are discussed.     

Effect of Water and Carbon Dioxide in Chemiluminescent Measurement of Oxides of Nitrogen

ABSTRACT

This paper reports results of studies using a biotrickling filter with blast-furnace slag packings (sizes = 2–4 cm and specific surface area = 120 m²/m³) for treatment of ethylether in air stream. Effects of volumetric loading, superficial gas velocity, empty bed gas retention time, recirculation liquid flow rate, and biofilm renewal on the ethylether removal efficiency and elimination capacity were tested. Results indicate that ethylether removal efficiencies of more than 95% were obtained with an empty bed retention time (EBRT) of 113 sec and loadings of lower than 70 g/m³/hr. At an EBRT of 57 sec, removal efficiencies of more than 90% could only be obtained with loadings of lower than 35 g/m³/hr. The maximum elimination capacities were 71 and 45 g/m³/hr for EBRT = 113 and 57 sec, respectively. The maximum ethylether elimination capacities were 71 and 96 g/m³/hr, respectively, before and after the renewal at EBRT = 113 sec. With an EBRT of 113 sec and a loading of lower than 38 g/m³/hr, the removal efficiency was nearly independent of the superficial liquid recirculation velocity in the range of 3.6 to 9.6 m³/m²/hr. From data regression, simplified mass-transfer limited, and reaction- and mass-transfer limited models correlating the contaminant concentration and the packing height were proposed and verified. The former model is applicable for cases of low influent contaminant concentrations or loadings, and the latter is applicable for cases of higher ones. Finally, CO₂ conversion efficiencies of approximately 90% for the influent ethylether were obtained. The value is comparable to data reported from other related studies.     

Superior Pillared Clay Catalysts for Selective Catalytic Reduction of Nitrogen Oxides for Power Plant Emission Control

ABSTRACT

Fe³+-, Cr³+-, Cu²+-, Mn²+-, Co²+-, and Ni²+-exchanged Al₂O₃-pillared interlayer clay (PILC) or TiO₂-PILC catalysts are investigated for the selective catalytic reduction (SCR) of nitric oxide by ammonia in the presence of excess oxygen. Fe³+-exchanged pillared clay is found to be the most active. The catalytic activity of Fe-TiO₂-PILC could be further improved by the addition of a small amount of cerium ions or cerium oxide. H₂O and SO₂ increase both the activity and the product selectivity to N₂. The maximum activity on the Ce-Fe-TiO₂-PILC is more than 3 times as active as that on a vanadium catalyst. Moreover, compared to the V₂O₅-WO₃/TiO₂ catalyst, the Fe-TiO₂-PILC catalysts show higher N₂/N₂O product selectivities and substantially lower activities (by ~85%) for SO₂ oxidation to SO₃ under the same reaction conditions. A 100-hr run in the presence of H₂O and SO₂ for the CeO₂/Fe-TiO₂-PILC catalyst showed no decrease in activity.     

Sources and Concentrations of Indoor Nitrogen Dioxide in Barcelona,Spain

Abstract

Sources and concentrations of indoor nitrogen dioxide (NO₂) were examined in Barcelona, Spain, during 1996– 1999. A total of 340 dwellings of infants participating in a hospital-based cohort study were selected from different areas of the city. Passive filter badges were used for indoor NO₂ measurement over 7–30 days. Dwelling inhabitants completed a questionnaire on housing characteristics and smoking habits. Data on outdoor NO₂ concentrations were available for the entire period of the study in the areas of the city where indoor concentrations were determined. Bivariate analysis was performed to investigate relationships between indoor NO₂ concentrations on one hand and outdoor NO₂ concentrations, housing, and occupant characteristics on the other. Stepwise multiple linear regression was performed with variables that were 1996 and 27.02 ppb in 1999, with the highest yearly value of 27.82 ppb in 1997. In the same time period, mean outdoor NO₂ concentration ranged between 25.26 and 25.78 ppb with a peak of 30.5 ppb in 1998. Multiple regression analysis showed that principal sources of indoor NO₂ concentrations were the use of a gas cooker, the absence of an extractor fan when cooking, and cigarette smoking. The absence of central heating was also associated with higher NO₂ concentrations. Finally, each ppb increase in outdoor NO₂ was associated with a 1% increase in indoor concentrations.     

海门市城区二氧化氮污染物浓度呈上升趋势的调查与分析

通过调查海门市城区所有NOX和NO2排放源,从排放情况和NO2月浓度变化情况分析,得出了海门市城区NO2污染物浓度呈上升趋势的结果。     

Ozone Control Strategies Based on the Ratio of Volatile Organic Compounds to Nitrogen Oxides

The 1990 Clean Air Act Amendments require states with O₃ nonattainment areas to adopt regulations to enforce reasonable available control technologies (RACT) for NO_X stationary sources by November 1992. However, if the states can demonstrate that such measures will have an adverse effect on air quality, NO_X requirements may be waived. To assist the states in making this decision, the U.S. EPA is attempting to develop guidelines for the states to use in deciding whether NO_X reductions will have a positive or negative impact on O3 air quality. Although NO_X is a precursor of O₃, at low VOC/NO_X ratios, the reduction of NO_X can result in increased peak O₃. EPA is examining existing information on VOC/NO_X ratios to develop “rules of thumb” to guide the states in their decision-making process. An examination of 6 a.m. to 9 a.m. VOC/NO_X ratios at a number of sites in the eastern U.S. indicates that the ratio is highly variable from day-to-day and there is no apparent relationship between ratios measured at different sites within the same area. In addition, statistical analysis failed to identify significant relationships between the 6 a.m. to 9 a.m. VOC/NO_X ratio and the maximum 1-hr. O₃ within a given area. Since we know from smog chamber and modeling studies that such a relationship exists, this further invalidates the assumption that a ratio measured at a single site is representative of the ratio for the entire region. Based on this Information, we conclude that having the 6 a.m. to 9 a.m. ambient VOC/NO_X ratio for a given area is insufficient information, by itself, to decide whether a VOC-alone, a NO_x-alone, or a combined VOC-NO_X reduction strategy is a viable or optimum O₃-reduction strategy.     

A Statistical Assessment of Saturation and Mobile Sampling Strategies to Estimate Long-Term Average Concentrations across Urban Areast

Abstract

The objectives of this study were: (1) to quantify the errors associated with saturation air quality monitoring in estimating the long-term (i.e., annual and 5 yr) mean at a given site from four 2-week measurements, once per season; and (2) to develop a sampling strategy to guide the deployment of mobile air quality facilities for characterizing intraurban gradients of air pollutants, that is, to determine how often a given location should be visited to obtain relatively accurate estimates of the mean air pollutant concentrations. Computer simulations were conducted by randomly sampling ambient monitoring data collected in six Canadian cities at a variety of settings (e.g., population-based sites, near-roadway sites). The 5-yr (1998–2002) dataset consisted of hourly measurements of nitric oxide (NO), nitrogen dioxide (NO₂), oxides of nitrogen (NO_x), sulfur dioxide (SO₂), coarse particulate matter (PM₁₀), fine particulate matter (PM_2.5)_, and CO. The strategy of randomly selecting one 2-week measurement per season to determine the annual or long-term average concentration yields estimates within 30% of the true value 95% of the time for NO₂, PM₁₀ and NO_x. Larger errors, up to 50%, are expected for NO, SO₂, PM_2.5, and CO. Combining concentrations from 85 random 1-hr visits per season provides annual and 5-yr average estimates within 30% of the true value with good confidence. Overall, the magnitude of error in the estimates was strongly correlated with the variability of the pollutant. A better estimation can be expected for pollutants known to be less temporally variable and/or over geographic areas where concentrations are less variable. By using multiple sites located in different settings, the relationships determined for estimation error versus number of measurement periods used to determine long-term average are expected to realistically portray the true distribution. Thus, the results should be a good indication of the potential errors one could expect in a variety of different cities, particularly in more northern latitudes.